Again and again, we have been asked the question concerning the difference between a complete pressure measurement and a gauge pressure measurement. To answer this question it helps to look at this is of gauge pressure and absolute pressure. The difference between the two measurements is then explained relatively simply and therefore also the decision of the appropriate measurement.
Definition of absolute pressure
Absolute pressure is really a pressure that is relative to the zero pressure in the empty, air-free space of the universe. Naked is the ideal or absolute vacuum. It is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure means the difference between an absolute pressure (Pabs) and the prevailing atmospheric pressure (Pamb). It really is denoted with the subscript ?e?: Pe and is calculated the following: Pe = Pabs ? Pamb.
Absolute vs gauge pressure measurement
The difference between the two measurements is relatively easily clarified: in a gauge pressure measurement, it is usually the difference from the existing ambient pressure that is measured. However, this pressure changes with the elements and the height above sea level. A complete pressure measurement measures the difference from the ideal or absolute vacuum. Because of this , this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is currently the right one?
In practice, both measurements could be differentiated as follows: usually, the measuring task would be to determine the gauge pressure. This is exactly why this type of sensor is hottest. However, in case a gauge pressure sensor is used in an application where the actual measuring task is to measure the absolute pressure, the next additional errors should be expected:
+/- 30 mbar caused by changes in weather
up to 200 mbar when changing the positioning (e.g. from sea level to 2,000 m)
With regards to the measuring range, these errors can be substantial (e.g. in pneumatics at a measuring selection of 1 bar) or negligible (in hydraulics at 400 bar).
Note
For anyone who is uncertain whether your measuring task needs an absolute pressure or gauge pressure measurement, simply contact us ? we?ll be glad to assist you.